A planar type X-ray detector based on an active matrix has been developed as a new-generation X-ray diagnosis detector. By detecting the X-ray applied to this X-ray detector, an X-ray imaged image or an X-ray image of real time are output as a digital signal. In the X-ray detector, the X-ray is converted to visible light, namely, fluorescence by a scintillator layer, and the fluorescence is converted to a signal charge by a photoelectric conversion element such as an amorphous silicon (a-Si) photodiode or CCD (Charge Coupled Device), and thereby an image is acquired.
A material of the scintillator layer generally includes cesium iodide (CsI):sodium (Na), cesium iodide (CsI):thallium (Tl), sodium iodide (NaI), or oxysulfide gadolinium (Gd2O2S). Gd2O2S is formed by mixing powder of sintered body with a binder resin and film coating, or used as an integrated sintered body. A method of improving resolution is conceived by forming a groove on these coated films or the sintered body by dicing or the like. The resolution characteristics of the CsI:Tl film and the CsI:Na film can be improved by causing a columnar structure to be formed by a vacuum deposition. A material of a scintillator includes various types described above and is used differently depending on application and necessary characteristics.
A reflection film may be formed on an upper portion of the scintillator layer in order to increase utilization efficiency of fluorescence and improve sensitivity characteristics. That is, fluorescence entering a photoelectric converter side is increased by reflecting fluorescence toward an opposite side to the photoelectric converter side of fluorescence emitted from the scintillator layer by the reflection film.
As an example of the reflection film, a method of forming a metal layer having a high fluorescence reflectance such as a silver alloy and aluminum on the scintillator layer, and a method of forming by applying a light scattering reflective reflection film made of a binder resin and a light scattering substance such as TiO2 are known. A method of reflecting scintillator light by causing a reflection plate having a metal surface such as aluminum to adhere to the scintillator layer instead of forming on the scintillator film is also put to practical use.
A moisture-proof structure for suppressing degradation of characteristics due to humidity or the like by protecting the scintillator layer, the reflection layer, or the reflection plate or the like from external atmosphere is an important constituent feature for making the detector a practical product. Particularly, in the case where the CsI:Tl film and the CsI:Na film which are highly degradative materials to the humidity are used as the scintillator layer, high moisture-proof performance is required.
The moisture-proof structure includes a method of using a CVD film of polyparaxylylene or a structure of surrounding the surrounding of the scintillator with an enclosure member to seal by combination with a moisture-proof layer or the like. As a structure capable of obtaining further high moisture-proof performance, a structure of processing an aluminum foil or the like having excellent moisture-proof performance into a hat-shape including the scintillator layer and sealing with a bonding layer at a periphery of the scintillator is known.